1. Field of the Invention
The present invention relates generally to a nonvolatile semiconductor memory device, and more particularly to a flash memory with a floating gate.
2. Description of the Related Art
Various structures and fabrication techniques relating to flash memories with floating gates have been proposed. Jpn. Pat. Appln. KOKAI Publication No. 2002-176114, for instance, discloses a nonvolatile semiconductor memory device wherein the gate structure of a transistor, other than a memory cell transistor, has the same stacked-gate structure as the memory cell transistor. In this nonvolatile semiconductor memory device, the gate structure is configured such that a floating gate and a control gate are connected via an opening, i.e. a slit, that is formed in an ONO film.
When such a slit is formed in the ONO film, however, the width of the slit varies greatly, leading to difficulty in control of dimensions. Thus, an exact slit width cannot be obtained.